AGRONOMIJAS VĒSTIS - Latvijas Lauksaimniecības universitāte

AGRONOMIJAS VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008cultivation and rototilling before sowing in spring. Given fertilisers: 34 kg ha -1 P, 75 kg ha -1 K and148 kg ha -1 N (18+70+60). Planting was carried out with by hand handled planter at 3 – 4 cmdepth. Weeds were controlled spraying herbicides (nicosulfuron 1.0 L ha -1 + dicamba 0.3 L ha -1 )and mechanically. Harvesting was done at four different times (factor C) beginning with1 September at ten day intervals. Yield was accounted from 0.7 m 2 on 1, 10 and 30 September andfrom 8.4 m 2 during the main harvest time on 20 September. Following observations were carriedout: field germination, flowering (tasseling and silking), plant density before harvest, plants per ha,plant height before harvesting, m, (data are not presented), green and dry matter (DM) yield, t ha -1 ,DM yield of corn-cobs, t ha -1 , and proportion of corn-cob DM yield in the whole plant DM yield, gkg -1 . For detecting the corn-cob yield, covering leaves of corn-cobs were peeled. Following qualityanalyses for every hybrid and in every harvest time were carried out using standard methods:content of DM of whole plant and corn-cobs, g kg -1 (Forage analyses met 2.2.1.1.); crude protein(CP), g kg -1 of DM (ISO 5983); neutral detergent fibre (NDF), g kg -1 of DM (Forage analyses met2.2.1.1.) and acid detergent fibre (ADF), g kg -1 of DM, (Forage analyses met 4.1.); ash (ISO 5984),Ca (ISO 5490/2) and P (ISO 6491), in g kg -1 of DM (data are not presented). Some parameterswere calculated in addition: digestible dry matter DDM g kg -1 = 889 – (0.779 x ADF); net energyfor lactation NEL MJ kg -1 of DM = (0.00245 x DDM - 0.12) x 4.184; dry matter intake DMI g kg -1of cow body weight = 12000/NDF. As they are derived from NDF and ADF data are not presented.Meteorological conditions were variable in the research years, and the main indices, average dailytemperature and precipitation, are characterized in Table 1.Table 1. Temperature and precipitation compared with meteorological norm during 2002-2004MonthAverage daily air temperature, °CPrecipitation, mm2005 2006 Norm 2005 2006 NormApril 6.0 5.8 4.9 17.2 20.4 42May 11.2 11.6 11.2 43.0 27.6 43June 14.3 16.2 15.1 48.6 24.2 51July 18.3 20.1 16.6 65.0 13.0 75August 16.1 17.5 16.0 106.4 150.0 75September 13.3 13.9 11.5 35.6 46.0 59Spring frost after maize emergence in research field was observed in 1 June 2006; plants werestressed and due to this herbicide spray was delayed; mechanical weed control was used in additionthus favouring moisture losses from soil and drought stress for plants. Strong fall frosts duringSeptember were observed on 17, 18 September 2005 – maize was frost-bitten. Summarisingmeteorological description, one could say that better suitable for maize growing and more typicalfor Latvia was year 2005; 2006 was atypical due to critically dry conditions; in July 2006 yield wasreally endangered.Results were statistically analysed using analysis of variance.ResultsOn average per trial maize DM yield was 2.06 t ha -1 higher in 2005 (14.17 t ha -1 ) ifcompared with yield in 2006 (12.11 tha -1 ). Our results showed strong harvest time effect onobtained maize yield (p